Dealkylation of alkoxyaryls



Patented Dec. 6, 1949 Bernard:W.- Rottschaefer, East-:GreenbusmhN; Y.,.assignor to. General Aniline &.;F;ilm Corporal tion, New York, Y.,a..cornorationpf.Delae ware.

NoiDrawinga ApplicationaIill'y 35 19463 SerialLNo. 681312 6 Claims.

Thewpresent invention relates to sa-method; of dealkylating alkoxyarylsand is particularly concerned with an improved method in which anal.-koxyaryl compound (especially analkoxy arylamino compound)v isdealkylated by treatment with a Friedel-Crafts reagent inasaturated-all.- phatic or alicyclic hydrocarbon solvent free, fromunsaturates and aromatics.

The use of a Eriedel-Crafits reagent as a dealkylating agent forthedealkylation of alkoxy aryls has heretofore been suggested. However,such prior art processes have-generally beenaccompanied by the formationof tarsandgums. I have now found that if the aromatic solvents. (such asbenzene, toluene and the. like) which have heretofore been employed,are. replaced by. a saturated aliphatic or alicyclic hydrocarbon me.-dium free from unsatunates and aromatics, the. dealkylation ofalkoxyaryl compounds. using. a Friedel-Crafts reagent is readilycarriediout with a goodyield of the desired product in a high degree ofpurity and'free of tars and other undesirable lay-products. I have alsofound that somewhat smaller amounts of Friedel-Crafts reagent can beemployed and in-the'case of alkox-yaryl amines, the reaction can becarried outemploying the free base instead ofrthe salt .ofthe base.

The process of the present invention is applicableto the dealkylationofcompoundsrepresented :by the following-general formula:

in which R represents an aromatic-hydrocarbon ring which may be eithermono-cyclic or polycyclic and-which may contain suchnuclear-substituents as alkyl, aryl, halogen; hydroxy, alkoxy; nitro,amino and the-like, but whichispreferably free of aryloxy substituents.As examples of such compoundsmay be mentioned anisol, anisi-- dine,phenetole. phenetidine, guaiacol, dianisidine and the like.

In practicing the process of this invention, the alkoxyaryl compound tobe dealkylated is dissolved or suspended in a saturated aliphatic oralicyclic hydrocarbon solvent free from unsaturates and aromatics. Anysaturated hydrocarbon which is liquid at the reaction conditions may beemployed as the solvent for the reaction. As examples of suitablesolvents may be mentioned methylcyclohexane, heptane, octane, nonane andvarious petroleum fractions free of unsaturates and aromatics. Asuitable solvent can readily be prepared by treating a gasoline orsimilar liquid petroleum fraction with approximately an equal volume ofsulfuric acid in order to remove any unsaturat-es or: aromatics;whicnit': may; contain. In orderl to; avoid-the "use;ofzilre ssur.e,-;vilhiS-z (18811:- a-blepthat the solvent; employed, have: anx. initialboiling point; of.:'at-.least-.:9.0..' C... Attheasame; time; too high.aiboiling solvent :is :pref-enablyi-avoidedr-in order; that thesolvent'lmay;readilyrbe recovered by distillation. I therefore. preferablemployras solvent a saturated, hydrocarbon boiling within the range ofapproximately -150 C. The relative amount. of fsolvent' employed duringvthe reaction' isnot;'highlyicritical so long as'a sufficient amountiis.used that thereactionrniittureas read ilyfluid:

In ordersto efiectihe *dealkylationoflthealkoxy aryl compounddissolvedion-suspendeddn=the-saia uratedi' hydrocarbon solvent, a1FriedelI-Crafts reagent iszadded toxwthermixturezof alkoxyaryl com:-pound; and solvent; preferably: atiuartemperature below about: 50?--C... and; the; reacti m mixture is then heated toa'temperatureatwhich:thedesired dealkylaitionz reactionz. proceeds at as satisfactoryrate,but below that at which undesirediseconde ary reactions takemlace. A.temperature of at least approximately 90 ,C. is preferred in ordertorobtain a satisfactory rate or reaction; while temperatures :muchxaibovet C. are preferabl-m avoide dcin .order to lpreventundesirableside rea'ce tionsh If'thessolvent:employedfior the'reaction resfluxesgwithlna range'vofiabout llof CT-to 150 C; the reaction mayadvantageouslybe carried outiat at mospheric.pressurezandflat;therefluxtempenature of, the solvent; However; superatmospheric.. pres--sure; may be employed: if. necessary in order" to maintaintheimaterialin; liquid phase.

As a.Frie.delCraftsmeagentI preferably employaluminum chloride orbromide; The relative amount: of; Friedel-Crafts: reagents employed willvary with i the; specific reagenmuseds. lip-general, the.-- approximateamoi-intv of oneumol. aluminum chlorideis employed per: an equivalent:of alkoxy exceptwhere; an-active. group-such as-ran :a-mine group ispresent, in which; case an. additionalequivalen-t quantity ofFriedel-Cnafts reagent is used. For example, when dealkylating phenctol,only one mol aluminum chloride need be used. However, in the case ofdianisidine, four mols of aluminum chloride are used, two tion indealkylating the two methoxy groups present, and two for reaction withthe two amine groups present.

The following examples describe in detail spetc fific preferredembodiments of the present invenion.

Example I A gasoline fraction which refluxed at approxifor consumpmately100l10 C. was refluxed for several hours with an equal volume of 100%H2804 in order to remove any unsaturated or aromatic hydrocarbons whichit might have contained, and was then separated from the H2s04 layer. To2,000 cc. of the saturated hydrocarbon thus obtained there were added244 grams (1 mol) of dry dianisidine and 580 grams (4.36 mols) ofanhydrous aluminum chloride were then added at a temperature ofapproximately 50 C. The material was then gradually heated to reflux(100-110 C.) and was refluxed for approximately '6 hours to complete thereaction. The charge'wa's then poured into 7,000 cc. of water containing4 mols of hydrochloric acid. The solvent was removed by steamdistillation and the charge diluted to approximately 8 liters. Theproduct-3,3-dihydroxy benzidinewas completely dissolved in the acidmother liquor and an traces of impurities were removed by treating withcharcoal and filtering.

--The 3,3-dihydroxy benzidine was then recovered from the acid motherliquor in the form of its sparingly soluble sulfate by adding about 800grams of NazSOa to the mother liquor and cooling to room temperature. Bythis procedure a very pure grade of 3,3-dihydroxy benzidine was obtainedin excellent yield.

Example II I 142.5 grams of 5-chloro-o-anisidine were added to 2,000 cc.oi gasoline fraction treated as described'in Example I. There were thenadded 267 grams (2 mols) of anhydrous aluminum chloride at a temperaturof approximately 45 C. The charge was then gradually raised to reflux(125 C.) and refluxed for 6 hours to complete the reaction. The chargewas then drowned into water containing an excess of hydrochloric acidand the gasoline removed by steam distillation. Theproduct-4-chloro-o-aminophenolwas recovered in excellent yield bycrystallization from the acid mother liquor. Example III 244 grams '(1mol) f dry dianisidine and 533 grams (4 mole), of anhydrous aluminumchloride were added to,2,000.cc..of methylcyclohexane at atemperaturegoi approximately 50 C. The material,- was then graduallyheated to reflux and was refluxed for approximately 6 hours to completethe reaction." The charge was then poured into 7,000 cc. of watercontaining 4 mols of hydrochloric acid. The solvent was removed by steamdistillation and the charge diluted to approximately 8 liters. Theproduct3,3-dihydroxybenzidine-was purified as in Example I.

It will be understood that the foregoing examples are illustrative onlyof preferred embodiments of the present invention and variousmodifications within the limits heretofore specified may be made thereinwithout departing from the teachings-of this invention.

I claim:

1. The process of dealkylating alkcxy andamino compounds free of aryloxygroups, which comprises heating to a temperature of 90-150 C. in a.distillable saturated hydrocarbon liquid a mixture of said alkoxyaryl-amino compound and an aluminum halide Friedei-Crafts agent in suchmolar proportions that one mol of said Friedel- Crafts agent is presentfor each alkoxy and amino group in said alkoxy aryl-amino compound.

2. The process of dealkylating alkoxy arylamino compounds free ofaryloxy groups, which comprises heating to a temperature of 90-150 C.,in a saturated hydrocarbon liquid boiling within the range of about90150 C., a. mixture of said alkoxy aryl-amino compound and an aluminumhalide Friedel-Crafts agent in such smaller proportions that 1 mol ofsaid Friedel-Crafts agent is present for each alkoxy aryl-amino group insaid alkoxy aryl-amino compound.

3. The process as defined in claim 2 wherein the aluminum halidespecified is aluminum chloride.

4. The process of dealkylating anisidine, which comprises refluxing in asaturated hydrocarbon liquid boiling at from 90-150 C, a mixture ofanisidine and an aluminum halide Friedel-Crafts agent in a molar ratioof 1 :2.

5. The process of producing 3,3'-dihydroxy benzidine by dealkylatingdianisidine, which comprises refluxing in a saturated hydrocarbon liquidboiling at from 90-150 C. a mixture of dianisidine and an aluminumhalide Friedel-Crafts agent in a Y molar ratio of 1:4.

6. The process of producing 4-chloro-o-aminophenol by dealkylating5-chloro-o-anisidine, which comprises refluxing in a saturatedhydrocarbon liquid boiling at from 90-150 C. a mixture of5-chloro-o-anisidine and an aluminum halide Friedel-Crafts agent in amolar ratio of 1:2.

BERNARD W. ROTTSCHAEFER.

REFERENCES CITED The following references are of record in the file ofthis patent:

FOREIGN PATENTS OTHER REFERENCES Hartmann et al., Ber. Deut. Chem, vol.25,

Ullmann et al., Ber. Deut. Chem, vol 39, pp. 622-625 (1906).

Oesterlein, Monatsh. vol. 57, pp. 31-44 (1931) Fernholtz et al., J. Am.Chem. Soc, vol. 60, p. 2404 (1938).

